There has been recently increasing interest in energy storage technology. As electrochemical devices have been widely used as energy sources in portable phones, camcorders, notebook PCs and electric cars, an effort on research and development of the electrochemical devices has been gradually actualized. In this regard, electrochemical devices are the subject of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention. Also, in developing such batteries, research on the design of a novel electrode and battery has been recently conducted in order to improve capacity density and specific energy.
Among the currently used secondary batteries, lithium secondary batteries, developed in early 1990's, are spotlighted because they generally have a high operating voltage and a considerably high energy density, compared to conventional batteries using aqueous electrolytes (such as Ni-MH batteries, Ni—Cd batteries, H2SO4—Pb batteries, etc.).
A lithium secondary battery is generally manufactured by employing materials capable of intercalating/deintercalating lithium ions as a cathode and an anode, and filling an organic electrolyte or a polymer electrolyte between the cathode and the anode. A lithium secondary battery generates electrical energy by an oxidation reaction and a reduction reaction when the lithium ions are intercalated and deintercalated from the cathode and the anode.
At present, as an electrode active material constituting the anode of the lithium secondary battery, a carbonaceous material is mainly used. However, in order to further improve the capacity of the lithium secondary battery, it is necessary to use a high capacity electrode active material.
In order to satisfy this requirement, for example, some metals (such as Si, Sn, or the like) which show a higher charge/discharge capacity than the carbonaceous material and can be electrochemically alloyed with lithium may be used as an electrode active material. However, such a metal-based electrode active material is subjected to a significant volume change according to the charge/discharge of lithium so that the metal-based electrode active material is cracked and pulverized. Thus, a secondary battery using such a metal-based electrode active material has problems, such as a sudden reduction in a capacity, and a reduction in a cycle life, as a charge/discharge cycle is repeated.
Accordingly, in order to complement cracks and pulverization occurring during use of the metal-based electrode active material, there has been suggested the use of a composite including a metal, such as Si, Sn, or the like, and oxide thereof as an electrode active material. However, the electrode active material employing the composite shows a high life characteristic and a high thickness controlling capability due to the metal oxide inhibiting cracks and pulverization of a metal, compared to the above mentioned metal-based electrode active material, while the improved extent is not much higher than expected.